Method of repairing worn valve guide apertures

ABSTRACT

The valve stem guide holes in the head of an internal combustion engine are enlarged in axial alignment with the axes of the original guide holes through the use of a reamer. The reamer employs a lead shank of substantially equal diameter to the valve stems, and of sufficient length to extend through the major portion of the length of these holes. The reamer is of proper diameter to enlarge the holes to accept a bushing or bearing sleeve through which the valve stem may slide. In the event the central portions of the valve guide holes are worn, a knurling tool may be first used to reduce the internal diameter of the hole, providing a guide for the lead shank of the reamer.

Jackson llll 3,802,055 [451' Apr.9, 1974 METHOD OF REPAIRING WORN VALVE GUIDE APERTURES Primary Examiner-Richard J. l-lerbst Assistant Examiner-D. C. Reiley, III Attorney, Agent, or F irm-Kenneth G. Jackson [5 7] ABSTRACT The valve stem guide holes in the head of an internal combustion engine are enlarged in axial alignment with the axes of the original guide holes through the use of a reamer. The reamer employs a lead shank of substantially equal diameter to the valve stems, and of sufficient length to extend through the major portion of the length of these holes. The reamer is of proper diameter to enlarge the holes to accept a bushing or bearing sleeve through which the valve stem may slide. In the event the central portions of the valve guide holes aretworn, a knurling tool may be first used to reduce the internal diameter of the hole, providing a guide for the lead shank of the reamer.

1 Claim, 6 Drawing Figures METIIOD OF REPAIRING WORN VALVE GUIDE APERTURES BACKGROUND OF THE INVENTION In the operation of internal combustion engines, there is a tendency for the guide holes in the engine head through which the stems of the valve slide to wear, enlarge, and to elongate. When this occurs, the valves do not seat properly, resulting in an improper operation of the engine. The only remedy, other than to obtain a new engine head which is identical to that originally used, is to bore out the holes, and to insert a bearing sleeve in the enlarged holes designed to slide ably accommodate the stems of the valves. Unfortunately, this is normally a difficult and time consuming operation. One of the reasons for this is that it is extremely difficult to perfectly align the re-bored hole with the original hole. Obviously, if the re-bored hole is not precisely concentric with the axis of the original hole, the valve cannot seat properly. Thus extreme care must normally be taken to perfectly center the tool used in drilling the enlarged holes. This is normally accomplished by mounting suitable fixtures on the undersurface of the engine head, perfectly aligning the guide fixtures with the valve holes, and then using these fixtures as a guide in boring the enlarged diameter hole. It is evident that a very considerable amount of time is required for perfectly boring each of the valve holes.

In normal operation of vehicle engine, the valve rods tend to elongate the guide holes in one direction or another. In other words, the means used for reciprocating the valve often tends to rock thevalvestems as they reciprocate, elongating the upper and lower ends of the guide apertures without greatly distorting the center areas of these holes. It has been found that even when the valve guide holes are badly worn or elongated at the ends of these holes, the center portionsof the holes fit the valve stemsquite accurately. Dependingupon the nature of the valve reciprocating means such as the tappets, the valve guide holes may be elongated on both sides of the true axis, or theelongation may take place at one end of the hole in one direction from the axis, and in the opposite direction from the axis at the other end of the hole. Thus in enlarging the holes, it is often difficult to ascertain the acutal axis of the original hole.

SUMMARY OF THE INVENTION I have found that original guide holes through the engine head may be readily drilled in an accurate manner by the use of a reaming tool including a concentric elongated lead shank which is of sufficient length to at least extend through the intermediate portion of the original guide hole. This lead shank is designed to extend through the portion of the hole which is least worn and acts as an accurate means of guiding the reamer through the hole. The portion of the reamer adjoining the lead shank is tapered to act as a drill, and the lead shankacts to guide the reamer through the head in precise alignment with the original axis of the hole.

In the event the central portion of the guide hole is also excessively worn, a knurling tool may be used which actually tends to form a threaded opening through the central portion of the guide hole. This knurling tool is not designed to cut the metal, but rather to force the metal between the threads of the knurling tool so that the resultant hole is of somewhat smaller diameter than prior to the use of the tool. This knurling tool thus acts to provide an elongated guide for the lead shank of the reamer to insure accuracy of the reamingioperation.

A feature of the present invention .resides in the method of forming'valve guide holes in an engine head which consists in knurling the inside of the hole, particularly at the relatively small diameter inner area thereof, thus forming an aperture of proper inner diameter to accommodate the lead shank of the reamer, and to use this guide portion or knurled portion to engage the lead portion of the shankand to center this lead portion with the original axis of the hole.

Some attempts have been made to use knurling tools to reduce the diameter of the valve guide holes and to thereby provide a proper guide for the valve stems. Ob viously, however, this is a temporary stop gap, as the ridges in the metal formed by the knurling tool quickly wear away and cause additional difficulty. As will be understood, afterthe guide hole has been reamed out,

a suitable bearing sleeve is inserted.- having proper internal diameter to snugly fit the valve. v

A further feature of the present invention lies in the provision of a lead shank which, in itself, is in the form of a reamer. If a knurling tool is used to decrease the inner diameter of the guide hole, the center section of the guide hole may be reduced in size to be. smaller than .the diameter of the lead shank. By providing reaming teeth on the lead shank, the guide hole may be first'reamed to the size of the valve stem, and then reamed to a largersize to accommodate the bushing or bearing.

These and other objects and novel features of the present invention will be more clearly and fully set forth in the following specification and claims.

BRIEF DESCRIPTION OF THEDRAWINGS FIG. 1 is a diagrammatic view of a knurling tool of FIG. 6 is a sectional view through a portion of the head showing the guide sleeve or bearing in place therein.

DESCRIPTION OF THE PREFERRED EMBODIMENT The present invention resides in the method and apparatus of drilling out valve guide holes in such a manner that they are concentric with the original valve stem guide holes through the ingine head. Accordingly, the engine itself is not shown, and the engine head itself may vary considerably in form and is only indicated in detailed section.

FIG. 3 of the drawings is a somewhat exaggerated view taken sectionally through the engine head, showing the manner in which the valve stem guide hole may elongate after use over an extended period of time. In this view, the engine head is indicated by the letter A, and the valve guide hole is indicated by the numeral 10. It will be noted that in most instances, the central portion 11 of the hole 10 shows a minimum amount of wear, in view of the fact that the valve stem tends to rock back and forth in a certain direction due to the action of the tappets. The action of the tappets may tend to elongate the upper and lower ends of the hole 10 on opposite sides of the central axis 12, or in some instances may elongate the ends of the holes in one direction only from the original axis. FIG. 3 indicates the hole 10 as being elongated on both directions from the original axis 12. v

. In the event the central portion 11 of the hole 10 is worn sufficiently to be considerably oversize, a knurling tool B may be used to decrease the effective size of the center portion of the hole. The knurling tool B includes a shank l3, and spiral threads such as 14. The tool B is not intended to remove metal from the walls of the aperture, but actually to force the metal inwardly between the threads 14 of the tool. In other words, the outer diameter of threads 14 are slightly greater than the diameter of the worn hole, and as the knurling tool is twisted through the hole, the metal which is displaced by the threads 14 is forced between the threads, thus actually slightly reducing the inner diameter of the hole and forming an aperture which is of slightly greater diameter than the valve stem. In other words, after the knurling'tool has been used, the center portion 11 of the hole 10 is capable of receiving the valve stem with a sliding fit. After the knurling has been used, the valve guide hole appears as indicated in FIG. 4, with the upper end 15 of the hole 10 and the lower end 16 thereof somewhat elongated, but the center portion of the hole concentric with the original axis thereof.

The reamer C is then used to enlarge the hole. The reamer C includes a lead shank 17 which is substan' tially the same diameter as the valve stem, so that this shank will fit snugly within the central portion of the hole 10. The angularly spaced reamer blades 19 are of somewhat larger diameter than the lead shank 17, and the lower end of the reamer teeth are deviled or angled as indicated at 20 so as to act as a drill. Thus, when the lead shank 17 is inserted into the hole 10, as indicated in FIG. 50f the drawings, the reamer blades 19 are forced through the hole, the angled blade ends 20 drilling the hole, and the blades 19 reaming it to a perfect cylindrical form concentric with the original axis of the hole.

In some instances the use of the knurling tool will reduce the diameter of the central portion of the guide hole to less than the diameter of the lead shank. Accordingly, the lead shank is provided with angularly spaced reamer blades or teeth 21 which, in the form illustrated, extend spirally at least a portion of the leading end of the lead shank. The end extremity of the lead shank is slightly tapered as indicated at 22. The reamer teeth 21 ream the guide hole to the valve stem diameter, and hold the reamer blades 19 centered with the original axis of the guide hole 10.

Once the original valve guide hole 10 has been properly enlarged, a bushing 23 is inserted into the aperture. The outside of the bushing or bearing 21 is of proper diameter to be press fitted into the enlarged aperture, and the inside diameter is of proper diameter to accommodate the valve stem. Each of the valve stem apertures is drilled out and bushed in the same manner, and the engine may be reassembled, with the valve centered with respect to the valve seats.

While the use of lead shanks on reamers is not completely new, in the past these shanks have been relatively short, the length of the shanks being only sufficient to extend into the apertures which are to be reamed. In the present instance, the lead shanks are purposely made long enough to extend through the major portion of the relatively long valve guide openings so that the reamer will be centered with the center portions of these openings rather than the end portions thereof. As a result, the holes maybe enlarged throughout their lengths in accurate relation to the original axes of the holes regardless of the direction of elongation of the ends of the holes. With the type of reamer described, the holes may be drilled through the use of a portable drill without the use of guiding fixtures thus greatly reducing the time required to complete the operation. In accordance with the Patent Statutes l'have described the principles of construction and operation of my Method and Apparatus for Relining Valve Guide Apertures, and while I have endeavored to set forth the best embodiments thereof, I desire to have it understood that obvious changes may be made within the scope of the following claims without departing from the spirit of my invention.

I claim: l

l. The method of repairing worn valve stem guide holes in the head of an internal combustion engine through the use of a reamer having an elongated lead shank adapted to extend at least the major portion of the length of the valve guide holes, and a knurling tool having a thread base diameter substantially equal to the valve stems of the valves used in these holes, the method consisting in:

knurling the valve guide hole to reduce the internal diameter of at least a portion thereof to approximately the exterior diameter of the valve stems, inserting the lead shank through the knurled portion of the hole for alignment therewith, v rotating the reamer to drill and ream an enlarged hole in axial alignment with the original valve stem guidehole, and inserting a bearing sleeve in the enlarged hole thus formed. 

1. The method of repairing worn valve stem guide holes in the head of an internal combustion engine through the use of a reamer having an elongated lead shank adapted to extend at least the major portion of the length of the valve guide holes, and a knurling tool having a thread base diameter substantially equal to the valve stems of the valves used in these holes, the method consisting in: knurling the valve guide hole to reduce the internal diameter of at least a portion thereof to approximately the exterior diameter of the valve stems, inserting the lead shank through the knurled portion of the hole for alignment therewith, rotating the reamer to drill and ream an enlarged hole in axial alignment with the original valve stem guide hole, and inserting a bearing sleeve in the enlarged hole thus formed. 